Long ago, the use of a single brake to provide both the main braking of the load and to control the descent of heavy strings of pipe in oil well drilling and servicing operations proved to be unsatisfactory. Since then, a brake system having both a main and an auxiliary brake has been used in oil well drilling and servicing operations to control the winch or drawwork when heavy strings of pipe are being lowered into the borehole in the earth.
Experienced oil well operators prefer the band brake as the main brake since it allows the operator to "feel" the loading. For example, any sudden decrease in the loading "felt" in the band brake is an indication to the operator that an obstruction has been hit in the borehole or that the load has reached the bottom of the borehole. The use of an auxiliary hydrodynamic brake has increased over the years. Parmac, Inc. of Coffeyville, Kans. sells an auxiliary hydrodynamic brake used with a conventional band brake under the trademarks "Hydromatic" or "Hydrotarder".
However, a conventional auxiliary hydrodynamic brake requires a fluid supply ranging from 300-500 gallons for operation of the brake. Therefore, using a system with an auxiliary hydrodynamic brake increases the total weight of the brake system at least 2400 lbs. for a normal 300 gallon tank. For a vehicle moving the well servicing equipment including the brake system from one location to another this could make the difference between complying with public road and bridge weight restrictions. Also, the preferred fluid used in a hydrodynamic brake is a water and antifreeze mixture. In recent years, environmental concerns and regulations have created a toxic waste disposal problem of this type of mixture, as well as concerns over accidental spills.
Other known brake systems in oil well servicing operations include a main disk brake sold by Galaxy of Canada in combination with an auxiliary hydrodynamic brake. U.S. Pat. No. 1,746,372 discloses an elevator brake system using a main external shoe friction brake in combination with an auxiliary hydrodynamic brake.
U.S. Pat. Nos. 1,985,889; 1,992,910; 1,992,911 and 1,992,912 disclose the use of an auxiliary hydrodynamic brake to control the speed of descent of a loaded winch or drawworks of a rotary drill rig while the load is stopped or held in the desired position by a main mechanical or solid friction brake. U.S. Pat. Nos. 1,985,889; 1,992,910; 1,992,911; and 1,992,912 are incorporated herein by reference for all purposes. U.S. Pat. No. 1,985,889 also discloses that the hydrodynamic brake may be mounted on the primary shaft or mounted on an auxiliary shaft. In particular, U.S. Pat. Nos. 1,992,910; 1,992,911 and 1,992,912 disclose a brake system for drilling equipment where a main external contracting band brake or "prony" brake is used for stopping the load and/or holding it at a desired position. This external contracting band brake is used in combination with an auxiliary hydrodynamic brake for controlling the speed of descent of cables employed with oil well drilling equipment.
U.S. Pat. Nos. 2,113,109; 2,126,751; 2,170,128; and 2,287,130 disclose an auxiliary hydrodynamic brake used on heavy vehicles, such as trucks and buses. These hydrodynamic brakes are used in combination with the conventional friction brakes on a vehicle used to bring the vehicle to a complete stop. The auxiliary hydrodynamic brake is adapted for retarding the movement of the vehicle and/or for determining a maximum rate of movement. For example, the hydrodynamic brake used in combination with the conventional friction brakes is intended to limit the speed of heavy vehicles when descending grades, as in hilly and mountainous country, without the necessity of the driver having to constantly employ the conventional friction brakes for this purpose.
No where in the prior art has a preferred main band brake been used in combination with an auxiliary disk brake where the disk brake is used for controlling the speed of descent of a winch cable employed with oil well drilling or servicing equipment. A brake system for an oil well rig using a conventional band brake with an auxiliary disk brake would provide ease of maintenance and repair. Also, the disk brake would not have the problem of liquid seals leaking nor would rotors or stators deteriorate as in the hydrodynamic brake.
Moreover, an auxiliary disk brake would remove environmental concerns of toxic waste disposal and accidental spills. The auxiliary disk brake would also reduce the weight of the brake system to comply with road and bridge restrictions and facilitate moving the brake system to locations where transportation is generally difficult.